Tracked down one of the more elusive bugs...

Symptoms:
While reading a file from SCSI in GPL mode, the system freezes upon finishing the file read.  

TEST PROGRAM IN XB:
1 OPEN #1:"SCS1.TESTDV",INPUT
2. INPUT #1:A$ :: PRINT A$ :: GOTO 2

When end of file is met, the program will halt with IO ERROR 25. Any action which causes the system to CLOSE the file results in a lockup.

Modifying the program in the following manner will pre-empt the lockup condition.  
1 OPEN #1:"SCS1.TESTDV",INPUT
2. INPUT #1:A$ :: PRINT A$ :: IF EOF(1)=0 THEN 2 ELSE CLOSE #1

CAUSE:
Within the file read/close routine in \HD.WINDS6-S is the following code : 
-----
READ
WRITE
*  FIRST FIND IF FILE OPEN
       CI   R2,WBUFEN
       JNE  ISOP              BRANCH IF ALREADY OPEN
* NOW TEST IF DISKETTE OR WINCHESTER
CLRE2  LI   R0,>E000
       CB   @PATHNM,@CHARW    IS IT WINCHESTER?
       JEQ  NOTOPN            YES, SO BOMB, BUT PASS ON CALL OTHERWISE
       B    @FLPRTN           BRANCH IF FLOPPY
*
NOTOPN B    @BADOP

----

Unfortunately, the check for "Winchester" which is really checking the pathname for "HD"  (short for HDSx") drops into the floppy routine if HD is not found.  Therefore, when the SCSI device is encountered, the DSR attempts to return to the floppy flush code, and locks the system. 

Modifying the code to include a test for SCS device fixed the problem short-term.  Overall restructuring of the DSR to separate floppy and 'fixed' devices is preferable though daunting.

FINAL TEST:
Using the same XB test above, reading past EOF generates an IO error 25 for all devices.  With the fix in place, IO Error 17 is generated for both SCSI and HFDC devices.

Tim